A fuel cell is like a battery that converts chemical energy originating from fuel oxidation to electric energy. In a hydrogen-oxygen fuel cell system, the hydrogen can be replaced with a gas fuel including methane and liquefied natural gas, or replaced with a liquid fuel including methanol.
In order to obtain power from a fuel cell stack of the fuel cell system, the temperature of the fuel cell stack must be more than a predetermined temperature, for example 50° C. If the temperature of the fuel cell stack is lower than the predetermined temperature, a membrane or a separating board of the fuel cell can be damaged, i.e. the temperature of the fuel cell increases rapidly so that thermal shock can occur. Accordingly, the efficiency of the fuel cell deteriorates.
Furthermore, although the relative humidity of the hydrogen, which is supplied at ambient temperature, is controlled to be 100%, as the reaction temperature inside of the fuel cell stack increases, the relative humidity of the hydrogen decreases, again deteriorating the efficiency of the fuel cell.
In a fuel cell system, methods for increasing reaction temperature and cooling water temperature are suggested as follows.
(1) Increasing the cooling water temperature by hydrogen combustion
(2) Increasing the cooling water temperature by methanol combustion
(3) Using an EHC (Electric Heated Catalyst)
(4) Increasing the reaction temperature by a reaction of hydrogen with oxygen near the MEA (Membrane Electrode Assembly)
The method of hydrogen or methanol combustion can easily increase the cooling water temperature by the heat of combustion. However, the methods of hydrogen or methanol combustion necessitate fuel consumption, so that the fuel consumption rate increases considerably. Furthermore, this method of hydrogen combustion has an associated danger of explosion.
The method of using an EHC (Electric Heated Catalyst) has a simple construction, but it has a defect in that a large quantity of electricity is consumed.
Finally, the method of using the reaction between hydrogen and oxygen near the MEA (Membrane Electrode Assembly) increases the reaction temperature rapidly so that the power is generated quickly, but an electrode catalyst can be damaged by thermal shock.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.